We are investigating how cells interact in a harmonious way over long distances via a diffusible chemotactile agent and via direct cell-cell contacts. The model system in question is D. discoideum, an amoebae, which under defined conditions, migrates chemotactically toward central collection points where they establish the intercellular connections basic to the formation of a multicellular organism. Our immediate approach to understanding how these cells process sensory information leading to a locomotory response is to study the regulation of the plasma membrane receptor for the chemotactic agent of these cells, cAMP. In the current year, we will continue our attempt to purify and characterize this receptor.